Field of the Invention
The present invention relates to a technique of recognizing another communication apparatus in a communication apparatus.
Description of the Related Art
In recent years, a wireless LAN represented by the IEEE802.11 standard series has been widely used. In the wireless LAN, a base station called an access point (AP) often controls a network. A wireless network is formed by the AP and stations (STAs) which fall within the radio wave coverage of the AP and are in a wirelessly connected state.
Furthermore, products and standards for various network forms of the wireless LAN have appeared on the market, in addition to this conventional simple wireless network configuration of the AP and STAs. U.S. Patent Application Publication No. 2014/0302787 describes NAN (Neighbor Awareness Networking) which has been defined by Wi-Fi Alliance as a standard for discovering a communication apparatus and a service provided by it with low power consumption. This is intended to reduce the power consumption when a communication apparatus synchronizes with another communication apparatus in terms of a period during which information is exchanged with the other communication apparatus, and thus shortens the time during which a wireless RF (Radio Frequency) part is enabled. This synchronization period in NAN is called a DW (Discovery Window). A set of NAN devices which share a predetermined synchronization period is called a NAN cluster. Among the NAN devices, terminals respectively having a master role or a non-master sync role transmit sync beacons as signals for ensuring the synchronization between the terminals during the DW period. The NAN device establishes synchronization with another terminal, and then transmits/receives a subscribe message as a signal for discovering a service, a publish message as a signal for sending a notification of provision of a service, and the like during the DW period. Furthermore, the NAN device can transmit/receive a follow-up message for exchanging additional information about a service during the DW period. On the other hand, the NAN device can enter a DOZE state as a state in which no wireless signal is received during the DW period, thereby reducing the power consumption.
The appearance frequency of DW periods during which a NAN device receives wireless signals depends on the NAN device but all NAN devices joining a NAN cluster need to receive wireless signals during a special DW period called DW0. DW0 indicates a DW period which comes once every 16 DW periods. Furthermore, DW0 indicates a DW period which starts when the lower 23 bits of a TSF (Time Synchronization Function) as a counter timer used by the NAN cluster for synchronization are 0×0. The NAN devices respectively operating in a master role or a non-master sync role need to transmit synch beacons for every DW period, and can thus receive wireless signals during all the DW periods.
If a NAN device is in the DOZE state during a DW period, it cannot transmit/receive a subscribe message and publish message during that period. This poses a problem that a period until another apparatus discovers a service provided by a NAN device which often enters the DOZE state during DW periods is prolonged.
The present invention provides a technique for shortening a period until a communication apparatus discovers another apparatus and a service provided by it.